1. Technical Field of the Invention
The present invention relates to mobile communications systems and, in particular, to the establishment of data/fax communications connections with a dual mode (analog/digital) mobile telephone.
2. Description of Related Art
Reference is now made to FIG. 1 wherein there is shown a block diagram illustrating a prior art system connection between an analog mobile telephone 10 and a supporting telecommunications network 12 to handle data/fax calls. Such data/fax calls are either originated at, or terminated to, a first piece of data terminal equipment 14(1) (such as a personal computer or a facsimile machine) connected to the analog mobile-telephone 10. At the other end of such an established data/fax call connection through the supporting telecommunications network 12 is a second piece of data terminal equipment 14(2) (also comprising, for example, a personal computer or a facsimile machine) that is connected to either another mobile telephone (not shown) or to land telephone line (also not explicitly shown). The supporting telecommunications network 12 in this instance comprises at least the public land mobile network (analog PLMN, such as an advanced mobile phone service (AMPS) system like that defined by the US EIA/TIA-553 standard) servicing the analog mobile telephone 10 and, where necessary, the network 12 further includes the public switched telephone network (PSTN).
The analog mobile telephone 10 is connected to the first piece of data terminal equipment 14(1) using an analog interface 16. Both the first and second pieces of data terminal equipment 14 include an integrated modem 18 for converting between a serial digital bit stream (compatible with the operation of the data terminal equipment) and an analog signal. This conversion is made through the implementation of standard, conventional PSTN modem protocols (such as V.34). This analog signal is of the type suitable for handling by either the analog mobile telephone 10 or a land line type PSTN 12 connection (not shown).
The communications connection between the analog mobile telephone 10 and the supporting PLMN 12 is effectuated over a cellular analog air interface 20 well known in the art. More particularly, the data/fax call itself is carried by an analog voice channel (AVC) 22 supported by the air interface 20.
Operation of the system connection illustrated in FIG. 1 is as follows. For data/fax information originated at the first piece of data terminal equipment 14(1), the generated serial digital bit stream is converted to the analog signal by the modem 18 using conventional PSTN modem protocols. The analog signal is then communicated by the analog mobile station 10 over the air interface on a selected analog voice channel. The supporting PLMN/PSTN 12 receives the transmitted analog signal, and routes the analog signal towards the destination second piece of data terminal equipment 14(2). A modem 18 within that second piece of data terminal equipment 14(2) then converts the analog signal to a serial digital bit stream for further processing. A reverse process is implemented for the communication of data/fax information originated at the second piece of data terminal equipment 14(2). In each case, an end-to-end connection through the supporting PLMN/PSTN 12 is established prior to any data/fax communication.
The reliability and robustness of data/fax calls carried over air interface 20 analog voice channels 22 using conventional PSTN modem protocols leaves much to be desired. A number of new enhanced analog data protocols (such as, for example, MNP10, ETC, TX-CEL, and the like cellular modem protocols) recently have been developed which significantly improve data throughput and reliability on analog voice channels. In order to take advantage of these enhanced two-sided protocols in the communications environment of FIG. 1, end-to-end support of the protocols must be available. Thus, each of the modems 18, rather than supporting only conventional PSTN modem protocols, must be able to support the enhanced protocols. Alternatively, as illustrated in FIG. 1, where the modem 18 connected to the second piece of data terminal equipment 14(2) supports only standard-PSTN modem protocols, the supporting PLMN/PSTN includes a configuration whereby a modem pool (MP) 24 is deployed within the network 12 to terminate the enhanced protocols utilized to facilitate analog air interface 20 (analog voice channel 22) data/fax communication, and provide an interworking towards the far end data terminal equipment 14(2) using the conventional PSTN modem protocols supported by its modem 18.
Operation of the system connection illustrated in FIG. 2 is as follows. For data/fax information originated at the first piece of data terminal equipment 14(1), the generated serial digital bit stream is converted to the analog signal by the modem 18 using one of the enhanced modem protocols. The analog signal is then communicated by the analog mobile station 10 over the air interface on a selected analog voice channel. The supporting PLMN/PSTN 12 receives the transmitted analog signal, and routes the analog signal towards the modem pool 24. Processing of the analog signal to terminate the enhanced modem protocols and apply the conventional PSTN modem protocols is then performed by the modem pool 24. The resulting signal is then routed through the network 12 to a destination second piece-of data terminal equipment (not shown, see, FIG. 1). The modem (not shown, see, FIG. 1) associated with that second piece of data terminal equipment then converts the analog signal to a serial digital bit stream for further processing. For these mobile originated calls, a special dialing procedure may be required in order to invoke the modem protocol conversion (i.e., interworking) functionality provided by modem pool 24. A reverse process is implemented for data/fax information originated at the second piece of data terminal equipment. However, for such mobile terminated calls, modem pool 24 configurations are not easily supported, and effective communication may be limited to a system connection providing end-to-end connectivity using only a selected one of the enhanced protocols.
Reference is now made to FIG. 3 wherein there is shown a block diagram illustrating a prior art system connection between a digital mobile telephone 40 and a supporting telecommunications network 42 to handle data/fax calls. Such data/fax calls are either originated at, or terminated to a first piece of data terminal equipment 44(1) (such as a personal computer or a facsimile machine) connected to the digital mobile telephone 40. At the other end of such a call connection through the supporting telecommunications network 42 is a second piece of data terminal equipment 44(2) (also comprising, for example, a personal computer or a facsimile machine) that is connected to either another mobile telephone (not shown) or to a land telephone line (also not explicitly shown). The supporting telecommunications network 42 in this instance comprises at least the public land mobile network (digital PLMN, such as a D-AMPS system like that defined by Interim Standard IS-54B/IS-136A) servicing the digital mobile telephone 40 and, where necessary, the network 42 further includes the public switched telephone network (PSTN).
The digital mobile telephone 40 is connected to the first piece of data terminal equipment 44(1) using a digital interface 46. In the event the second piece of data terminal equipment 44(2) utilizes a wireless or wireline analog connection to the supporting network 42, an integrated modem 48 is included for converting between a serial digital bit stream (compatible with the operation of the data terminal equipment) and an analog signal through the implementation of standard, conventional PSTN modem protocols. This analeg signal is of the type suitable for handling by either the analog mobile telephone 10 (see, FIG. 1) or a land line type PSTN 42 connection (not shown).
The communications connection between the digital mobile telephone 40 and the supporting PLMN 42 is effectuated over a cellular digital air interface 50 well known in the art (such as the Interim Standard IS-136 interface). More particularly, the data/fax call itself is carried by a digital traffic channel (DTC) 52 supported by the air interface 50. The D-AMPS portion of the network 42 supports an Asynchronous Data and Group 3 Fax (ADS/G3Fax) service capability which allows mobile subscribers to originate or terminate modem based data calls using these digital traffic channels 52. For data/fax calls, the conventional PSTN modem protocol utilizes phase shift keyed (PSK) tones to transmit information. These tones are not suitable for processing by the vocoder (not shown) within the digital mobile station 40. A digital radio link protocol (RLP, such as the Interim Standard IS-130 protocol) is provided over the air interface 50 to obviate the need for a modem and support serial digital bit stream communication with the first piece of data terminal equipment 44(1) using the digital traffic channel 52. Furthermore, the supporting PLMN/PSTN 42 includes an interworking functionality (IWF) 56 operable to terminate the radio link protocol utilized for the air interface 50 connection and support interworking with the far end data terminal equipment 44(2) using the conventional PSTN modem protocols (or perhaps other enhanced modem protocols) supported by its modem 48. Appropriate use of the Interim Standard IS-737 protocols (providing network ANSI 41 message support) is also made.
Operation of the system connection illustrated in FIG. 3 is as follows. For data/fax information originated at the first piece of data terminal equipment 44(1), the generated serial digital bit stream is transmitted to the digital mobile station 40 and communicated over the air interface 50 on a selected digital traffic channel 52. In this implementation, the information bypasses the vocoder (not shown) of the digital mobile station 50, and the appropriate radio link protocol is applied to support the call. The supporting PLMN/PSTN 52 receives the transmitted digital signal, and routes the digital signal towards the --interworking function 56. Processing of the digital signal in order to terminate the applied radio link protocol and apply the conventional PSTN modem protocols (or perhaps other enhanced modem protocols) supported by the modem 48 for the far end data terminal equipment 44(2). The signal is then routed to that far end piece of data terminal equipment 44(2) through the network 42. The modem 48 then converts the received signal to a serial digital bit stream for further processing by the data terminal equipment 44(2). A reverse process is implemented for data/fax information originated at the second piece of data terminal equipment.